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United States Patent |
5,256,187
|
Gefvert
|
October 26, 1993
|
Separation of precious metals by an ion exchange process
Abstract
The present invention relates to the extraction and separation of low
concentrations of precious group metals from acid chloride solutions,
which are obtained by leaching catalytic converters, by utilizing a
8-hydroxyquinoline containing resin and a thiourea stripping process. The
said process eliminates the phase separation problems and reagent losses
which are normally associated with prior art methods. In addition to being
used as a catalytic converter recycler, the present invention can be also
employed by waste water treatment plants.
Inventors:
|
Gefvert; David L. (Dublin, OH)
|
Assignee:
|
Sherex Chemical Company, Inc. (Dublin, OH)
|
Appl. No.:
|
975062 |
Filed:
|
November 12, 1992 |
Current U.S. Class: |
75/717; 75/718; 75/720; 423/22; 423/24; 423/139 |
Intern'l Class: |
C22B 003/24 |
Field of Search: |
75/741,711,720,717,718
423/22,24,139
|
References Cited
U.S. Patent Documents
3637711 | Jan., 1972 | Budde, Jr. et al.
| |
3725046 | Apr., 1973 | Hartlage et al.
| |
3882053 | May., 1975 | Corte et al.
| |
3933872 | Jan., 1976 | Hartlage.
| |
3989650 | Nov., 1976 | Lange et al.
| |
4066652 | Jan., 1978 | Hartlage.
| |
4067802 | Jan., 1978 | Cronberg et al.
| |
4205048 | May., 1980 | Kyung et al.
| |
4389379 | Jun., 1983 | Rouillard epouse Bauer et al.
| |
4568526 | Feb., 1986 | Rouillard nee Bauer et al.
| |
4592779 | Jun., 1986 | Russ et al. | 75/741.
|
4654145 | Mar., 1987 | Demopoulos et al.
| |
4855114 | Aug., 1989 | Gefvert.
| |
4913730 | Apr., 1990 | Deschenes et al. | 75/720.
|
5134169 | Jul., 1992 | Green et al. | 210/688.
|
Other References
Pouskouleli, "Recovery and Separation of Platinum and Palladium by
coextraction and Differential Stripping", pp. 174-188. Separation
Processes in Hydrometallurgy Jul. 1987.
|
Primary Examiner: Andrews; Melvyn J.
Attorney, Agent or Firm: Scully, Scott, Murphy & Presser
Claims
What is claimed is:
1. In the extraction and separation of one or more precious metals selected
from the group consisting Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au and
mixtures thereof from a dilute aqueous chloride feed solution thereof
which also contains contaminant metal values, by contacting said feed
solution with an ion exchange resin to load said one or more precious
metals and contaminant metal values onto said resin and subsequently
stripping said one or more metals from the resin, the improvement
comprising
a) selectively eluting said contaminant metal values from the metal-loaded
ion exchange resin with deionized water or distilled water; and then
b) stripping the precious metals from said metal-loaded ion exchange resin
with an acidic thiourea stripping solution.
2. A process according to claim 1 wherein said precious metals are Pd and
Pt.
3. A process according to claim 2 wherein said feed solution contains from
about 1 to about 1000 ppm of Pt and from about 1 to about 1000 ppm of Pd.
4. A process according to claim 1 wherein said contaminant metal values are
selected from the group consisting of Pb, Al, Ba, Ce, Zr, Zn, Cu, Fe and
mixtures thereof.
5. A process according to claim 4 wherein said contaminant metal values
comprise about 0 to about 2000 ppm of Pb.
6. A process according to claim 4 wherein said ion-exchange resin comprises
a substituted or unsubstituted 8-hydroxyquinoline chelating agent.
7. A process according to claim 6 wherein said ion-exchange resin comprises
a 7-alkyl-8-hydroxyquinoline chelating agent.
8. A process according to claim 1 wherein said ion-exchange resin comprises
an iminodiacetic chelating agent.
9. A process according to claim 1 wherein said acidic thiourea solution
contains from about 1M to about 4M HCl.
10. A process according to claim 9 wherein said stripping solution contains
at least 0.01M thiourea.
11. A process according to claim 10 wherein said stripping solution
contains from about 0.01 to 2M thiourea.
12. A process according to claim 1, further comprising, following step (b),
separating a solid product comprising the stripped precious metal values
from said stripping solution.
13. A process according to claim 12 wherein said separating step comprises
hydrogen reduction of said solution to cause said solid product to form.
14. A process according to claim 12 wherein said separating step comprises
adding a precipitant to said stripping solution to cause said solid
product to form.
15. A process according to claim 14 wherein said precipitant is caustic
soda.
Description
FIELD OF THE INVENTION
The invention relates to an improved method for recovering precious metals
from various processing streams by employing a selective ion exchange
resin followed by subsequent stripping to remove essentially contaminant
free precious metals. A preferred aspect of the invention concerns the
recovery of lead-free Pd and Pt by using a 8-hydroxyquinoline treated
resin followed by elution of the precious metals by an acidic thiourea
stripping process.
BACKGROUND OF THE PRIOR ART
The increasing demand for platinum group metal use in industrial
applications has made an impact on the industrial practice of recovering
and refining precious methods. To meet this challenge, the classical
precipitation techniques are being abandoned for more modern separation
methods. Among the latter, solvent extraction (SX) has proven to be a
suitable and powerful separation technique for the precious group metals.
Briefly, solvent extraction comprises two steps. In the first, the
extraction step, dilute aqueous feed solution, containing the metal ion(s)
to be recovered, is mixed with an immiscible hydrocarbon diluent or
carrier containing a liquid ion exchanger or ligand dissolved therein, and
the resulting metal chelate migrates to the organic phase. In the second,
the stripping step, the separated "loaded" organic phase is mixed with an
aqueous solution of a stripping agent (e.g., sulfuric acid) and the
procedure is reversed, the metal ion passing back to the new aqueous
phase. As a consequence, the dilute feed solution is converted into a
highly concentrated solution, from which the metal values are more readily
recovered, e.g., by electrolysis.
Despite, however, the superior performance of the SX process, these methods
are not without their drawbacks The principal cause for their weaknesses
is that the reagents used are not necessarily compatible with PGM-bearing
feedstock solutions. In addition when the concentration of the desired
metals is low, recovery and separation of Pt and Pd using SX methods are
extremely difficult.
One way of overcoming these drawbacks is to employ an ion-exchange resin
which contains a complexing or extracting agent. In this case, the desired
precious metals are physically absorbed onto the resin and removal is
accomplished by acid washing.
The compound 8-hydroxyquinoline is well known for its ability to coordinate
with a variety of transition metal ions through covalent bonding to form a
stable 5-membered ring via metal chelation. Recently, however, the ability
of 8-hydroxyquinoline to form chelates with platinum group metals has been
employed in SX of feed streams containing such precious metals.
Unfortunately, this extracting agent is not sufficiently soluble in the
hydrocarbon solvents employed in the first step of the SX process, and it
is too soluble in the acidic aqueous stripping phases. The deficiencies of
8-hydroxyquinoline can be overcome by attaching 8-hydroxyquinoline to a
resin backbone.
Resins developed by Bayer in U.S. Pat. Nos. 3,882,053 and 3,989,650
contain aminoethyl terminated cross linked polymers. In DE Patent No.
50153.00A, the aminoalkyl terminated cross linked polymers are further
modified by condensation of these amines with 8-hydroxyquinoline and
aldehydes. This reaction results in a chemical bond between the
hydroxyquinoline and the resin. This chemically modified resin was then
used to extract precious group metals from their acid chloride feeds. The
said condensation discussed above is believed to generate additional
chelating sites on the resin; however, it was determined that Pt could not
be removed from the resin by normal water washing process.
A growing industrial concern involves the recovery of Pd, Pt and Rh from
spent automotive catalytic converters. Because of the low levels of such
precious metals and the high levels of contaminants found in the solutions
obtained by leaching catalytic converters, prior art methods do not offer
an efficient way of cleanly separating these metals. Additionally, these
methods usually result in a lead-contaminated Pt solution. Thus, it would
be extremely beneficial if a recovery process could be developed which can
separate low levels of precious metals, i.e. platinum group metals, and
eliminate contamination of the final solution.
SUMMARY OF THE INVENTION
The present invention relates to the extraction and separation of low
concentrations of precious metals from acid halide solutions which are
obtained by leaching catalytic converters, by utilizing a
8-hydroxyquinoline containing resin and a thiourea stripping process. The
said process eliminates the phase separation problems and reagent losses
which are normally associated with prior art methods. In addition to being
useful in recycling of metals used in e.g. catalytic converters, the
present invention can also be employed by waste water treatment plants.
DETAILED DESCRIPTION
The present invention provides a method for recovery of precious metals
from various process streams by employing a selective ion exchange resin
and a stripping step. The process is applicable to the treatment of acid
chloride solutions containing one or more precious metals selected from
the group consisting of iron, cobalt, nickel, copper, ruthenium, rhodium,
palladium, silver, osmium, iridium, platinum and gold and mixtures
thereof. A preferred embodiment of the invention relates to the recovery
of platinum, palladium and gold from acid chloride solutions. More
specifically, the invention described herein involves the recovery of Pt
and Pd from catalytic converters.
The said process is utilized for the extraction of said precious metals
from a dilute aqueous halide solution by contacting the solution with an
ion exchange type resin followed by subsequent stripping of the precious
metal values. It is a preferred embodiment of the invention that the ion
exchange resin contains chelating sites which allow for the selective
elution of lead and other contaminants. The elution of the precious metal
values from the lead-free resin is then accomplished by employing an
acidic thiourea solution.
The present invention can be applied to any level of precious metals
contained in the liquor. It is especially useful for the recovery of Pd
and Pt from chloride feed liquors containing from about 100 to about 300
ppm of Pt and from about 50 to about 100 ppm of Pd. In addition to the
precious metals, the chloride feed liquors may contain any combination of
metallic contaminants including any selected from the group consisting of
lead, aluminum, barium, cerium, zirconium, iron, copper and zinc.
The chloride feed liquors can result from treatment of precious group metal
slimes resulting from the electrorefining of copper, or treatment of
precious metal-containing scrap such as electronic circuit boards, plating
effluents, or refractory gold ore. As previously mentioned, the present
process is especially successful when the precious metal levels are low.
For example, the solutions obtained from the leaching of spent automobile
catalytic converters are well suited for this process.
The characteristics of feed liquors that can be treated by this process
have few limitations, provided that the feed liquor contains sufficient
amounts of halide ion to maintain the precious metal values in solution.
However, excess amounts of nitrating agents are not recommended since they
destroy the ability of the resins to perform normally.
The precious metal solutions are normally the result of oxidative chloride
leaching of the raw material. This involves first leaching the finely
divided material with a hydrochloric acid solution that contains an
oxidizing agent. Typical oxidizing agents that can be used include
hydrogen peroxide, chlorine, chlorate, perchlorate, and permanganate.
Another preferred embodiment of the invention is that the platinum should
be maintained in a +4 valence state whereas palladium and gold are
normally at +2 and +3 valence states respectively.
The resins suitable for the process of the invention must be substantially
insoluble in and essentially unaffected by the leaching solutions.
Additionally, the desired resin must have a chelating function
sufficiently strong to be able to form a complex with the precious metal
so that the metal values can be selectively removed from the feed.
Further, the resin must allow for the precious metals to be selectively
removed from the resin bed by thiourea elution process. The chelating
agent can be either physically or chemically deposited on the resin. It is
a preferred aspect of the invention that the chelating agent be attached
to the resin backbone by a covalent bond. This type of resin-chelate bond
assures that the chelating agent will not be removed during the extraction
or separation process. Chelating structures which are suited in this
process include 8-hydroxyquinoline and iminodiacetic acid or any
derivatives thereof. These agents are well known to form strong chelates
with precious group metals; however, they do not bind or chelate the
contaminants which may be present in the feed liquor. Therefore, cross
contamination of the mixture is avoided. Thus, the resin bed is
essentially free of contaminants prior to the stripping process.
One preferred resin used in this process contains iminodiacetic acid. This
polymer type resin is previously reported to contain a styrene
divinylbenzene copolymer having iminodiacetic acid functional groups
directly bonded to it. This particular resin is especially stable under
either acidic or basic conditions (i.e. pH 1-14).
In another preferred embodiment, a resin described in DE 50153.00A is
particularly preferred for use in this process. This resin is also a
polymer system which contains a styrene-divinylbenzene copolymer.
Additionally, 8-hydroxyquinoline is attached to this polymer backbone
through covalent bonding.
The resins employed by this process are usually conditioned prior to the
extraction process. This conditioning step involves a continuous washing
with about 2 to about 6M HCl until the effluent is essentially colorless.
The resin is then washed with deionized water until a neutral pH is
obtained.
The resin is then contacted with the solution from which it is desired that
the metal values be extracted. Contact can be batchwise, i.e., in a
reactor vessel that is preferably undergoing mild agitation, or
continuous, i.e., in a concurrent or countercurrent column. The relative
amount of resin to solution for effective extraction is readily
ascertained.
The chelated precious metal values are then washed off the resin by using a
thiourea stripping solution. Washing for a sufficient time with water
(deionized or doubly distilled) alone results in the removal of lead from
the resin but not the precious metals. Washing thereafter with an
appropriate acidified thiourea stripping solution results in removal of
the precious metals present from the resin backbone. It is preferred that
the thiourea solution contain from about 1 to about 6M HCl, especially
from about 2 to about 3M HCl. Another preferred embodiment of the present
invention is that the stripping solution contains from about 0.01 to about
2M thiourea, especially from about 0.1 to about 1M thiourea, in 2M HCl.
Other acids which can be used to dilute the thiourea besides HCl include
H.sub.2 SO.sub.4. This acidified thiourea solution is essentially
sufficient to remove the precious metals from the polymer backbone without
destroying the covalent bond between the chelating agent and the polymer
backbone of the resin described herein.
The precious metal values isolated by this process are in the form of
thiourea complexes in a solution containing HCl. The precious metals may
be precipitated from this acidic thiourea solution by the addition of a
strong alkaline solution, such as a solution of sodium hydroxide. The
precipitated metals can be redissolved in HCl to obtain concentrated
solutions free of contaminating base metals. The precious metals may then
be separated by means well known in the art. Alternatively, a precious
metal powder can be obtained by reducing the thiourea solution with
hydrogen. The thiourea solution can be recycled to stripping and the
precious metal alloy powder refined by conventional methods.
The following examples, which are for purposes of illustration and not
limitation, will further describe the invention.
SUMMARY OF TABLES
I. Represents The Analysis of Column Feed and Column Raffinate Solutions
for Pt, Pb and Pd.
II. Represents the Analysis of the Wash Water After Passing 700 ml of Acid
Chloride Solution Through The Column
III. Represents the Analysis of Column Feed and Column Raffinate Solution
for Pt, Pb and Pd.
IV. Determination of Optimal Thiourea Solution.
V. Determination of Optimal HCl Concentration in the Optimal Thiourea
Solution
VI. Determination of Optimal Thiourea Concentration in 2M HCl Solution
VII. Determination of Resin Bed Efficiency During the Stripping Process
EXAMPLE 1
Two grams of a polymer A based on iminodiacetic acid (IonacSR-5Sybron
Chemicals Inc.) were treated with 40 ml of a 3M HCl solution for 30 min.
and then washed thoroughly with water. Polymer A was then contacted with
11 ml of an acid leached solution for 2 hours. The leached solution
contained 100 ppm of Pt, 120 ppm of Pd and 315 ppm of Pb and was 2.5 ml in
HCl. After this time period, the system was filtered and the filtrate was
analyzed for levels of PGM. The filtrate was determined by chemical
analysis to contain 96 ppm of Pt, 70 ppm of Pd, and 250 ppm of Pb. This
indicates that a significant amount of Pd and Pb was extracted in this
process.
The filtered resin was then washed with 100 ml of deionized water for 1 hr.
and filtered. The filtrate contained no detectable amounts of Pt or Pd.
However, it was determined from the ppm of lead that water contact alone
was sufficient enough to strip the lead off the resin. Analysis of the
filtered resin showed a positive test for Pt and Pd; however, it was
negative for Pb.
The resin was then contacted with 0.2M thiourea and 2M HCl solution
resulting in removal of Pt and Pd from the resin into the thiourea
solution.
EXAMPLE 2
Resin B contained a 8-hydroxyquinoline structure which was covalently
bonded to the resin. This resin was reported in DE 50153.00A and is
uniquely suited for the process of this invention.
The resin was conditioned by continuous washing with 6M HCl until the
effluent was essentially colorless. It was then water washed until a
neutral pH was obtained. The resin was used in a column having sufficient
volume for 100 ml of the resin.
A monolithic spent catalytic converter was crushed into one inch cubes.
These cubes (approximately 250 g) were placed into a jacketed column of
700 ml capacity. The column was then heated to 100.degree. C. and the
leach liquor (6M HCl and 1% H.sub.2 O.sub.2) was pumped up the column at a
rate giving 70 min. retention time in the column. Leach liquor exiting the
leach column passed into the bottom of the column holding 100 ml of the
resin material.
At 100 ml aliquots, the leach liquor and raffinate (liquid exiting the
resin column) were analyzed for Pt, Pd and Pb. The analysis is shown in
Table I. The data illustrate that the column is essentially removing all
the Pt, Pd and Pb. At a bed volume of about 7, there is indication that
the Pb is being selectively crowded off the resin by Pd and Pt.
After 700 ml of leach liquor had passed through the resin column, the
resin-bed was washed with 1.0 l of deionized water and analyzed every 100
ml for Pt, Pb and Pd. The results are shown in Table II. The data
indicates a surprising selectivity for the removal of Pb from the resin by
the water wash process whereas the Pd and Pt are still strongly attached
to the resin. Thus, a clean separation of Pb from Pd and Pt using
8-hydroxyquinoline derivative is possible.
The resin bed containing Pt and Pd was then contacted with 2.1 l of fresh
feed liquor from the leach column. The results are shown in Table III.
Once again, the raffinate indicates that essentially all of the Pt and Pd
is being retained on the resin, but the Pb is being crowded off.
Next, the resin bed was water washed and removed from the column. The
analysis of the resin showed high levels of Pt and Pd with only trace
amounts of Fe and Sn contaminants were detected. More importantly,
however, was that no Pb was found.
A 3 gm sample of this resin was then treated with 50 ml of various
stripping solutions containing thiourea. The results of this study are
shown in Table IV. The water and H.sub.2 SO.sub.4 solutions of thiourea
show significant precipitation of precious group metal salts on standing.
To determine the optimum thiourea acidity, the following concentration of
HCl solutions containing 1M thiourea were tested (Table V). The data
indicates that the optimum thiourea acidity is a solution containing
approximately 3M HCl. At high acidity levels (6M HCl), a precipitate
formed during standing. The optimum thiourea content in a 2M HCl solution
was also determined. The results of this study are shown in Table VI.
The final study was conducted to determine the efficiency of the resin bed
stripping process. About 40 ml of resin containing 0.35 g Pt and 0.23 g Pd
was contacted with 0.1M thiourea in 2M HCl solution. Analysis after each
40 ml aliquot of stripping solution was acquired. The data of the
experiment is shown in Table VII. The results show the ability of the
thiourea solution to effectively remove PGM from the resin.
TABLE I
______________________________________
ANALYSIS OF COLUMN
FEED AND COLUMN RAFFINATE
Column Feed Column Raffinate
Bed Pt Pd Pb Pt Pd Pb
Volume (ppm) (ppm) (ppm) (ppm) (ppm) (ppm)
______________________________________
1 75 60 750 -- -- --
2 100 70 550 -- -- --
3 100 45 440 -- -- --
4 100 50 425 -- -- --
5 90 50 400 -- -- --
6 75 40 350 -- -- --
7 90 40 260 -- -- 100
______________________________________
TABLE II
______________________________________
ANALYSIS OF WASH WATER AFTER CONTACT
WITH RESIN LOADED WITH Pt, Pd, and Pb
Bed Volume Pt (ppm) Pd (ppm) Pb (ppm)
______________________________________
1 -- -- 100
2 -- -- 300
3 -- -- 575
4 -- -- NA*
5 -- -- 800
6 -- -- 350
7 -- -- 150
8 -- -- 50
9 -- -- 15
10 -- -- 10
______________________________________
*NA not analyzed
TABLE III
______________________________________
ANALYSIS OF COLUMN
FEED AND COLUMN RAFFINATE
Column Feed Column Raffinate
Bed Pt Pd Pb Pt Pd Pb
Volume (ppm) (ppm) (ppm) (ppm) (ppm) (ppm)
______________________________________
1 150 100 470 -- -- 100
2 100 75 300 -- -- 75
3 100 NA 40 -- NA 75
4 100 60 180 -- -- 60
5 90 40 175 -- -- 110
6 50 50 110 -- -- 160
7 60 45 120 -- -- 230
8 65 25 90 -- -- 220
9 -- 30 85 -- -- 225
10 -- 25 -- -- -- 180
11 -- 30 50 -- -- 150
12 -- 30 50 -- -- 150
13 -- -- 100 -- -- 150
15 -- -- -- -- -- 100
17 -- -- -- -- -- --
19 -- -- 50 -- -- --
21 -- -- -- -- -- --
______________________________________
NA = Not Analyzed
TABLE IV
______________________________________
DETERMINATION OF OPTIMAL
THIOUREA SOLUTION
Stripping Solution % Stripped
(1M thiourea dissolved in . . . )
Pt Pd
______________________________________
H.sub.2 O 68 80
H.sub.2 SO.sub.4 68 77
1 M HCl 81 91
2 M NaOH 2 0
______________________________________
TABLE V
______________________________________
DETERMINATION OF OPTIMAL HCl
CONCENTRATION IN THE THIOUREA
STRIPPING SOLUTION
Stripping Solution % Stripped Off
(in 1M thiourea) Pt Pd
______________________________________
1 M HCl 81 91
3 M HCL 84 93
6 M HCl 78 92
______________________________________
TABLE VI
______________________________________
DETERMINATION OF OPTIMAL THIOUREA
CONTENT IN A 2 M HCl SOLUTION
Stripping Solution
(in 2 M HCl thiourea % Stripped Off
concentration) Pt Pd
______________________________________
0.2 M 61 79
0.5 M 68 84
1.0 M 63 85
*1.0 M 92 99
______________________________________
*Experiment to determine whether a column strip responds better than a
batch stripping of the resin sample, the depleted resins of 0.2M and 0.5M
were again contacted with 1M thiourea yielding the observed results.
TABLE VII
______________________________________
DETERMINATION OF THE RESIN BED
EFFICIENCY DURING THE STRIPPING PROCESS
Aliquot Pt (ppm) Pd (ppm) Pb (ppm)
______________________________________
1 15 0 0
2 1200 1000 0
3 200 135 0
4 200 100 0
5 50 42 0
6 50 20 0
7 50 15 0
8 0 10 0
9 0 0 0
______________________________________
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